Herpes zoster in three healthy children immunized with varicella vaccine (Oka/Biken); the causative virus differed from vaccine strain on PCR analysis of the IV variable region (R5) and of a PstI-site region.

This study was undertaken to determine whether the causative virus was a vaccine-derived or wild-type virus when zoster occurred in healthy children immunized with varicella vaccine (Oka/Biken). The DNAs of clinical isolated strains and vaccine strain (Oka/Biken) were analyzed by the polymerase chain reaction with two sets of primers for the variable region IV (R5 tandem direct reiterations, TDR) and for the region with a PstI site in a middle portion of the long unique segment of the varicella zoster virus genome. Of six zoster patients after vaccination with Biken, three clinical isolates were examined and had two copies in R5 TDR and were PstI-site positive. Therefore, these strains were different from the vaccine-type strain (Oka/Biken), which had two copies in R5 TDR and was PstI-site-negative. The mean age of onset of zoster was 4 years. The mean age of vaccination was 25 months. The mean interval between vaccination and onset of zoster was 22 months. Hence the results indicate that the causative virus of zoster in healthy children immunized with varicella vaccine (Oka/Biken) was wild type and differed from the vaccine strain. Some vaccinees probably do not have protective immunity for a long time after immunization because the mean interval between vaccination and onset of zoster was 22 months.